1,104 research outputs found
Bounds on Heavy-to-Heavy Mesonic Form Factors
We provide upper and lower bounds on the form factors for B -> D, D^* by
utilizing inclusive heavy quark effective theory sum rules. These bounds are
calculated to leading order in Lambda_QCD/m_Q and alpha_s. The O(alpha_s^2
beta_0) corrections to the bounds at zero recoil are also presented. We compare
our bounds with some of the form factor models used in the literature. All the
models we investigated failed to fall within the bounds for the combination of
form factors (omega^2 - 1)/(4 omega)|omega h_{A2}+h_{A3}|^2.Comment: 27 pages, 10 figure
Form-factor-independent test of lepton universality in semileptonic heavy meson and baryon decays
In the semileptonic decays of heavy mesons and baryons, the lepton-mass dependence factors out in the quadratic cos2θ coefficient of the differential cosθ distribution. We call the corresponding normalized coefficient the convexity parameter. This observation opens the path to a test of lepton universality in semileptonic heavy meson and baryon decays that is independent of form-factor effects. By projecting out the quadratic rate coefficient, dividing out the lepton-mass-dependent factor, and restricting the phase space integration to the τ lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three (e,μ,τ) modes in a given semileptonic decay process. We discuss how the identity is spoiled by new physics effects. We discuss semileptonic heavy meson decays such as B¯0→D(∗)+ℓ-ν¯ℓ and Bc-→J/ψ(ηc)ℓ-ν¯ℓ and semileptonic heavy baryon decays such as Λb→Λcℓ-ν¯ℓ for each ℓ=e, μ, τ
Exclusive semileptonic decays of D and Ds mesons in the covariant confining quark model
Recently, the BESIII collaboration has reported numerous measurements of various D(s) meson
semileptonic decays with significantly improved precision. Together with similar studies carried out at
BABAR, Belle, and CLEO, new windows to a better understanding of weak and strong interactions
in the charm sector have been opened. In light of new experimental data, we review the theoretical
description and predictions for the semileptonic decays of D(s) to a pseudoscalar or a vector meson.
This review is essentially an extended discussion of our recently published results obtained in the
framework of the covariant confining quark model
Importance of Tests for the Complete Lorentz Structure of the t --> W+ b vertex at Hadron Colliders
The most general Lorentz-invariant decay-density-matrix for , or for , is expressed in terms
of eight helicity parameters. The parameters are physically defined in terms of
partial-width-intensities for polarized-final-states in decay.
The parameters are the partial width, the quark's chirality parameter
, the polarimetry parameter , a "pre-SSB" test parameter
, and four - interference parameters , ,
, which test for violation. They can be
used to test for non-CKM-type CP violation, anomalous 's, top
weak magnetism, weak electricity, and second-class currents. By stage-two
spin-correlation techniques, percent level statistical uncertainites are
typical for measurements at the Tevatron, and several mill level uncertainites
are typical at the LHC.Comment: Minor clarifications. Expression for r_{+-} corrected. 19 pages LaTex
+ Tables + 1 Figur
Gluon interference effects in t-tbar production at the Next Linear Collider
We study the effects of gluon interference in the production and
semi-leptonic decay of a t-tbar pair above threshold at the Next Linear
Collider (NLC). We calculate all matrix elements to next-to-leading order and
use the resulting expressions for the development of a Monte Carlo event
generator. Our results show effects at the level of 10% in differential
cross-sections. We thus extend previous results obtained by analytical means in
the soft-gluon limit.Comment: 20 pages, incl. 9 figures, LaTeX (revtex, eepic, axodraw
Feynman Rules for the Rational Part of the Standard Model One-loop Amplitudes in the 't Hooft-Veltman Scheme
We study Feynman rules for the rational part of the Standard Model
amplitudes at one-loop level in the 't Hooft-Veltman scheme.
Comparing our results for quantum chromodynamics and electroweak 1-loop
amplitudes with that obtained based on the Kreimer-Korner-Schilcher (KKS)
scheme, we find the latter result can be recovered when our
scheme becomes identical (by setting in our expressions)
with the KKS scheme. As an independent check, we also calculate Feynman rules
obtained in the KKS scheme, finding our results in complete agreement with
formulae presented in the literature. Our results, which are studied in two
different schemes, may be useful for clarifying the
problem in dimensional regularization. They are helpful to eliminate or find
ambiguities arising from different dimensional regularization schemes.Comment: Version published in JHEP, presentation improved, 41 pages, 10
figure
Some constraints on neutral heavy leptons from flavor-conserving decays of the Z boson
Small neutrino masses can arise in some grand unified models or superstring
theories. We consider a model with an enhanced fermion sector containing Dirac
neutral heavy leptons. The dependence on the mass and mixing parameters of
these new fermions is investigated for several measurable quantities. We study
the flavor-conserving leptonic decays of the Z boson and universality breaking
in these decays. We also consider the W boson mass dependence on neutral heavy
lepton parameters.Comment: 20 pages, Revtex 3.0, 6 uuencoded and compressed postscript figures
included. Compressed postscript file of paper, including figures, also
available by anonymous ftp at
ftp://ftp.physics.carleton.ca/pub/theory/gour/ocipc9411.ps.Z . Accepted for
publication in Phys. Rev. D
Phenomenology of neutral heavy leptons
We continue our previous work on the flavour-conserving leptonic decays of
the Z boson with neutral heavy leptons (NHL's) in the loops by considering box,
vertex, and self-energy diagrams for the muon decay. By inclusion of these
loops (they contribute to the input parameter M_W) we can probe the full
parameter space spanned by the so-called flavour-conserving mixing parameters
ee_(mix), \mu\mu_(mix), \tau\tau_(mix) in a superstring-inspired model of
neutrino mass. We compare the results of our analysis with the existing work in
this field and conclude that flavour-conserving decays have certain advantages
over traditionally considered flavour-violating ones.Comment: submitted to Phys. Rev. D, 30 pages, 9 figures (ps), REVTE
The NLO QCD Corrections to Meson Production in Decays
The decay width of to meson is evaluated at the next-to-leading
order(NLO) accuracy in strong interaction. Numerical calculation shows that the
NLO correction to this process is remarkable. The quantum
chromodynamics(QCD)renormalization scale dependence of the results is obviously
depressed, and hence the uncertainties lying in the leading order calculation
are reduced.Comment: 14 pages, 7 figures; references added; expressions and typos ammende
Heavy quark supermultiplet excitations
Lorentz covariant wave functions for meson and baryon supermultiplets are
simply derived by boosting representations corresponding to
multiquark systems at rest.Comment: 12 pages (Revtex), UTAS-PHYS-93-4
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